In recent years there has developed an increased concern regarding the transfer of disease, infection and the like to syringe users and healthcare professionals who accidentally or through negligent handling, stick themselves with hypodermic needles while disposing of used hypodermic needle. In many areas in a hospital, where needle cannula products are used, disposal bins are provided so that a syringe or other needle cannula product may be immediately discarded in a safe rigid container. However, there are areas of medical practice, such as emergency rooms, where disposal containers may not be readily available or practical, and where products having self-contained safety features are desirable. In theory, after such a syringe is used to inject medication or for another purpose, a safety device contained within the syringe or needle assembly is activated to prevent further contact with the sharp needle tip. One type of safety syringe includes structure which allows the withdrawal of the hypodermic needle into the syringe barrel to minimize the chance of further contact with the sharp needle tip.
The prior art includes retracting needle syringes which include a spring loaded needle assembly which is held in position during normal use of the syringe assembly and a hollow plunger rod which is sealed during normal use of the syringe assembly so that medication or other liquids may not enter the plunger rod cavity. These syringes must have structure to allow release of the spring-loaded needle and the opening of the plunger rod cavity so that the needle may enter the plunger rod cavity after the syringe is used for its intended purpose. To function properly, the cavity in the plunger rod must be sealed so that medication cannot enter into the plunger rod during use. This seal must sometimes withstand high hydraulic pressures when injecting relatively viscous medication through small needles and still be capable of being easily unsealed and to allow access by the needle assembly. Likewise, the needle assembly must be firmly held in place through the forces of injection and still be disengageable so that it may retract into the syringe barrel and into the plunger rod. Some of the prior art retracting needle syringes to solve these problems by providing a leak-proof physical structure for holding the spring-loaded needle in position and for sealing the end of the hollow plunger rod. Upon completion of the injection process additional distally directed force is applied to the plunger causing an internal cutting element to cut through the end of the hollow plunger rod and the support for the spring-loaded needle. In some embodiments, the prior art retracting needle syringe cutter cuts in a proximal direction through the support for the spring-loaded needle assembly and then through the distal end of the plunger rod. In both cases this allows the spring-loaded needle to enter the cavity in the plunger helping to keep the user safe from accidental needle sticks.
Prior art retracting needle syringes that rely on dislodgeable elements or the breaking of frangible barriers will allow the spring-loaded needle to enter into the plunger can require a broad range of forces to disengage the spring-loaded needle. Retracting needle syringes with the cutter have an inherent advantage of being capable of being made so that the forces necessary to activate the retracting needle are more consistent from syringe to syringe.
The present invention addresses an improved cutting element for a retracting needle syringe for providing even more consistent syringe to syringe activation forces and, if desired, lower activation forces.